Robotic assembly machines often utilize video cameras to observe the component, part or work piece being handled, machined or assembled. For instance, in the assembly of electronic components, the chips or wafers are often assembled into printed circuit boards by robots utilizing video cameras to position the components and/or to inspect the assembled device for defects throughout the process.
In the microelectronics industry, solder pads on surface-mount devices are often observed by machine vision systems for assembly and manufacturing purposes. The accuracy and reliability of a machine vision system is critical for proper alignment of the numerous components which are to be mounted on a printed circuit board. For optimum alignment, solder pads must be clearly observed in high contrast with their background.
Components in many industries often utilize etched characters appearing on mirror like surfaces that serve to identify the components and to accurately position them during assembly. In order to permit a clear image of the characters to be produced in the camera for accurate manipulation of the parts by the robotic handling equipment, it is important that the observed object be properly illuminated.
Proper illumination of many different shiny and uneven surfaces, e.g. solder connections, foil packaging, ball bearings, etc., is critical if high quality robotic assembly is to be achieved. However, such shiny and uneven surfaces are difficult to illuminate for accurate video imaging, and this creates a need for improved illumination of such objects being observed by machine vision cameras.
When using previously available illumination systems to illuminate work pieces having uneven, highly reflective surfaces, the uneven reflection of light from these surfaces frequently produces erroneous images and signals within the camera thereby possibly resulting in an erroneous signal or incorrect/inaccurate measurement. Errors of one or two thousands of an inch in a fiducial location measurement for a single component are sufficient to ruin a large and expensive circuit board. Furthermore, previously available illumination systems for robotic handling of items have not produced a light which is uniform over the entire object being observed. As a result, the reflected image suffers from erroneous shadows, glints and glare thereby rendering it difficult to determine the precise location or quality of the object.
To date, many illumination devices have been developed to provide substantially uniform illumination of an object to be viewed, but such known illumination devices are fairly large and cumbersome and are thus difficult to integrate into an electronic manufacturing process. For example, one of the Inventor's known light system might occupy a volume of 300 cubic inches and weigh several pounds, thereby adding to the costs and expense in constructing machine vision equipment in a very competitive industry. It is desirable to manufacture a miniature illumination device which may occupy 8 cubic inches or less and only weigh a few ounces. Such miniaturization allows significant cost savings and lessens the expense of the machinery for inspecting manufactured products.
The term "diffuse", as used in this patent application, means a light source which is uniformly dispersed over a broad range of incident angle of azimuth and elevation with respect to the object being observed, and the light source approaches complete coverage over the area where the light is directed, i.e. greater than 80% of the possible angular range of incident light--approaching area X in FIG. 12. The term "invisible", as used in this patent application when referring to the diffuser and the object to be observed, means that the surface emitting the diffused light from the diffuser is at an angle greater than a critical value with respect to the object such that that emitting surface can not directly illuminate the object, i.e. only indirect illumination of the object by reflection of light of the side wall(s) of the housing can occur.
Wherefore it is an object of the invention to overcome the above noted drawbacks of the prior art illumination devices.
It is another object of the present invention to develop an improved continuous diffuse illumination device for machine vision systems to precisely determine the location of the object being observed.
It is a further object of the invention to develop an improved diffuse wide angle illumination field to improve image quality and uniformity of appearance of uneven specular surfaces, such as those found in the electronic and pharmaceutical manufacturing processes, e.g. pills, capsules, and their packaging.
A still further object of the invention is to provide an adaptor for an existing diffuse illumination device that increases the uniformity of the illumination provided thereby.
Yet another object of the invention is to increase (e.g. double) the brightness of the light reflected by the beam splitter to make such reflected light appear more equal in brightness to the light reflected by the diffusely reflecting inner surfaces of the surrounding housing structure.
Yet another object of the invention is to reduce the brightness of the direct off-access light from the diffuser to the object to the same range of brightness as the light reflected by the beam splitter and the surrounding housing structure.
Still another object of the invention is to minimize uneven illumination of the object to be observed and the area adjacent the object, e.g. maximize the range of elevational angles of incident which commonly occur with simple beam-splitter illumination devices (Carr et al. for example) where the beam splitter is planar and its bottom edge is substantially flush with the bottom aperture of the housing.